Study Sheds New Light on Causes of Common STD

Oral sex may be a risk factor for nongonococcal urethritis (NGU), one of the most common sexually transmitted diseases affecting both men and women, according to a new study in the Feb. 1, 2006 issue of the Journal of Infectious Diseases, now available online.

 The study, by Australian researchers Catriona Bradshaw, MD, and colleagues at the Melbourne Sexual Health Centre, is the first major case-control study to simultaneously address all currently hypothesized causes of NGU. The findings help to identify areas for future research on the causes of NGU, and suggest that treatment decisions should be based on clinical features of the diseasenot just microscopic assessment.  The study also is the first to demonstrate that the causes of NGU in men who have sex with other men are similar to those found in heterosexual men.  

NGU is caused by a number of different organisms (most notably, Chlamydia trachomatis) and may lead to pelvic inflammatory disease, infertility, and chronic pelvic pain. Though the cause of NGU is sometimes known, and antibiotics (azithromycin or tetracycline) are generally effective, about half of all cases have no identifiable cause a fact that makes treatment frustrating and uncertain for physicians and patients. Results of previous studies show that Chlamydia trachomatis causes between 30 percent to 50 percent of cases of NGU and Mycoplasma genitalium, 10 percent to 30 percent.

From March 2004 to March 2005, the Melbourne team studied 329 men with NGU and 307 men without symptoms of urethritis. All subjects were given a sexual practice questionnaire. The men in the study underwent a urethral smear, and provided a first-stream urine specimen, which was tested for pathogens that may have caused NGU.

Chlamydial infection was common in both heterosexual and homosexual men with NGU (22 percent and 15 percent, respectively) and was far more common than in control groups. C. trachomatis and M. genitalium were associated with unprotected vaginal sex. M. genitalium (9 percent), adenoviruses (4 percent), and herpes simplex type 1 (2 percent) were more common in NGU patients than in controls, after adjusting for age and risk, which suggests that these organisms may be causes of NGU.

Adenoviruses and herpes simplex type 1 were associated with oral sex and sex between male partners, suggesting that oral-genital contact may be an important mechanism of NGU pathogen transmission. Additionally, NGU was associated with history of oral sex with new partners.  Together, these findings suggest that fellatio plays a significant role as a cause of the syndrome.

In an accompanying editorial, H. Hunter Handsfield, MD, of the BattelleCenter for Public Health Research and Evaluation and the University of Washington, called the landmark Melbourne study "a good interim step" whose findings "significantly advance the field," but points out that many important questions remain yet to be answered.

The study provides important insight for both heterosexual and homosexual men, as it indicates that NGU may be caused by otherwise harmless organisms shared by monogamous partners. According to Handsfield, this finding may influence clinical management of partners and counseling of couples. In addition, oral sex was associated with NGU in which no pathogen was detected, indicating that there are causes of NGU that have yet to be identified. The study also found that type 1 herpes simplex virus (HSV-1), the usual cause of oral herpes, accounted for more NGU cases than did HSV-2; that herpetic NGU was most commonly associated with fellatio; and that up to a third of NGU cases associated with known pathogens were not associated with increased numbers of white blood cells in urethral secretions.

Source: Infectious Diseases Society of America (IDSA)